RESEARCH/REVIEW ARTICLE Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia) Victor A. Zakharov,1 Mikhail A. Rogov,1 Oksana S. Dzyuba,2 Karel Zˇ a´ k,3 Martin Kosˇt’a´ k,4 Petr Pruner,3 Petr Skupien,5 Martin Chadima,3 Martin Mazuch4 & Boris L. Nikitenko2 1 Geological Institute of Russian Academy of Sciences, Pyzhevski lane, 7, Moscow RU-119017, Russia 2 Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of Russian Academy of Sciences, Acad. Koptyug av., 3, Novosibirsk RU-630090, Russia 3 Institute of Geology of the Academy of Sciences of the Czech Republic, v.v.i., Rozvojova´ 269, CZ-165 00 Prague 6, Czech Republic 4 Institute of Geology and Palaeontology, Faculty of Science, Charles University in Prague, Albertov 6, CZ-128 43 Prague 2, Czech Republic 5 Institute of Geological Engineering, Technical University of Ostrava, 17 listopadu 15, CZ-708 33, Ostrava-Poruba, Czech Republic Keywords Abstract Biodiversity; stable isotopes; J/K boundary; Arctic Realm; palaeoceanography. The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but Correspondence outside the Tethys such data are very scarce. Here we present results of a study Mikhail A. Rogov, Geological Institute of of the most complete section in the Panboreal Superrealm, the Nordvik Russian Academy of Sciences, Pyzhevski section. Belemnite d18O data show an irregular decrease from values reaching lane, 7, Moscow, RU-119017, Russia. up to 1.6 in the Middle Oxfordian and from 0.8 to 1.7 in the basal E-mail: [email protected] Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon d13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem. The J/K boundary interval was characterized by re- at outcrops (Smith & McGowan 2007). This suggests a markable palaeoceanographic and palaeoenvironmental continual biotic turnover caused partly by palaeoceano- changes in Europe (Tremolada et al. 2006), but in contrast graphic changes and, especially, large palaeogeographic to other system boundaries it was not connected to a events (Raup & Sepkoski 1982; Sepkoski 2002; Keller global extinction event. The decrease in marine family 2008). In the Arctic Realm, the transition between the diversity at the J/K boundary was estimated to lie between Jurassic and Cretaceous was connected with neither 5.1 and 6.5% (Hallam & Wignall 1997), while the de- extinction nor a radical reorganization in marine biota crease in generic diversity of all marine animals was less (Zakharov et al. 1993). This view is supported by faunal than 10% (Rogov 2013). Moreover, even this extinc- analysis (Dzyuba 2013; Rogov 2013) that indicated an tion rate could be overestimated due to the incomplete increase in ammonite and belemnite diversity. However, databases used, high evolutionary rates in Tithonian on a global scale, the tectonic movements at the end of ammonites, time-averaging (Rogov 2013) and tapho- the Jurassic led to closure of many seaways and further nomic features (i.e., a presence of numerous Lagersta¨tten differentiation of the Panboreal and TethysÁPantalassa of KimmeridgianÁTithonian age and a scarcity of earliest superrealms (Gasin´ ski 1997). Following proposals by Cretaceous ones), along with well-known relations of fau- Westermann (2000), names and ranges of these units nal diversity and the surface area of sediments surviving were subsequently adjusted. Polar Research 2014. # 2014 V.A. Zakharov et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial 3.0 1 Unported License (http://creativecommons.org/licenses/by-nc/3.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Citation: Polar Research 2014, 33, 19714, http://dx.doi.org/10.3402/polar.v33.19714 (page number not for citation purpose) Palaeoenvironments and palaeoceanography changes across the J/K boundary V.A. Zakharov et al. In the Panboreal Superrealm, there is no section where stratigraphic framework make this profile most suitable sedimentation patterns and biostratigraphy of the J/K for a palaeocological and palaeoceanographic investiga- boundary interval are represented more completely than tion of the Arctic Realm. in a section on the Nordvik Peninsula (north-eastern Siberia; Fig. 1). On the Nordvik Peninsula, the Laptev Sea Geological settings and palaeogeographic cliff exposes a continuous succession of silty mudstones aspects spanning the Middle Oxfordian to Upper Valanginian. The boreal ammonite and buchiid successions are recog- The Nordvik section is one of the most comprehensively nized in great detail from the Middle Oxfordian to the top studied Jurassic sections in the Russian Arctic. It has been of the section (Zaharov et al. 1983; Zakharov & Rogov studied in detail by sedimentologists, geochemists, phy- 2008; Rogov & Wierzbowski 2009). A belemnite biostratig- sicists and biostratigraphers (Zaharov & Judovnyj 1974). raphy is well developed for the Middle OxfordianÁLower The OxfordianÁRyazanian part of this section has been Ryazanian interval (Dzuˆ ba 2004; Dzyuba 2012). Foramini- subdivided biostratigraphically by means of ammonites fers and marine palynomorphs from the Middle Volgian (Zaharov et al. 1983; Zakharov & Rogov 2008; Rogov to the Lower Valanginian have been studied in detail by & Wierzbowski 2009), belemnites (Dzuˆ ba 2004; Dzyuba Nikitenko et al. (2008). 2012), buchiid bivalves (Zaharov et al. 1983), foramini- Here we present results of an integrated study that fers and dinoflagellate cysts (Nikitenko et al. 2008, 2011). includes an analysis of changes in assemblages (including A remarkable positive d13C excursion (carbonate in bel- relative abundance) of all major fossil groups and an emnite rostra), which is considered as a useful marker analysis of sea-level oscillations. An earlier investigation for the Panboreal and BorealÁTethyan correlation of of stable isotope data derived from belemnite rostra J/K boundary beds, has recently been recorded in the (Zˇ a´k et al. 2011; Dzyuba et al. 2013) was complemented Nordvik section in the top part of the Taimyrensis Zone by analysing the d13C values of bulk organic matter. (Dzyuba et al. 2013). Major aims of this integrated study include the determi- The Nordvik Peninsula is located in the eastern part of nation of biodiversity changes across the J/K boundary the YeniseiÁKhatanga basin (Fig. 2) which is a part of the and the identification of possible relationships between Mesozoic depression extending from the Yenisei River different environmental factors, including sea-level os- mouth to the Lena River mouth along the northern cillations, palaeoclimate, oxygen level in the sea water margin of the Siberian platform (Saks et al. 1959). In the and biodiversity changes. south, the YeniseiÁKhatanga basin is bounded by the The unique original high-latitude palaeogeographic northern edge of the platform which is covered by position (see Housˇa et al. 2007) of the investigated section Palaeozoic and Lower Triassic deposits. In the west, it was quite far from the coastline. The complete sedimen- is connected with the UstÁYenisei basin. In the east, tary succession without major hiatii and the precise the YeniseiÁKhatanga basin reaches the LenaÁAnabar Fig. 1 Palaeogeographic and geographic position of the Nordvik section. 2 Citation: Polar Research 2014, 33, 19714, http://dx.doi.org/10.3402/polar.v33.19714 (page number not for citation purpose) V.A. Zakharov et al. Palaeoenvironments and palaeoceanography changes across the J/K boundary Fig. 2 Palaeogeography and facial succession in the YeniseiÁKhatanga Strait during the Jurassic/Cretaceous transitional time (modified after Zaharov & Sˇ urygin 1983). (a) Detailed palaeogeography of the YeniseiÁKhatanga Strait during the Ryazanian. Land area is indicated in beige. Bionomic marine zones are marked by Roman numerals: I, deep-water; II, moderately deep-water; III, shallow water. (b) Facies profile through the YeniseiÁKhatanga Strait and changes in bivalve and foraminiferal assemblages. basin, being separated from it by a buried uplift. The The basement of the YeniseiÁKhatanga basin is com- latter continues as a projection of the Siberian plat- posed of Palaeozoic and volcanogenic Lower Triassic form between the Popigai and Anabar rivers towards the rocks. The basin is primarily filled by marine Jurassic to Anabar Gulf. lowermost Hauterivian deposits, and in the west overlain Citation: Polar Research 2014, 33, 19714, http://dx.doi.org/10.3402/polar.v33.19714 3 (page number not for citation purpose) Palaeoenvironments and palaeoceanography changes across the J/K boundary V.A. Zakharov et al. Fig. 3 (Continued) 4 Citation: Polar Research 2014, 33, 19714, http://dx.doi.org/10.3402/polar.v33.19714 (page number not for citation purpose) V.A. Zakharov et al. Palaeoenvironments and palaeoceanography changes